Aggregate testing

Which tests does an aggregate testing suite usually include?

A typical suite covers grading, particle shape, fines content, water absorption, particle density, resistance to fragmentation and soundness or freeze-thaw where durability has to be proved. Which of those you actually need is set by the product standard and the end use, not by the material itself. A producer proving a new source generally needs the full set, while a contractor checking a delivered stockpile usually needs far fewer.

Which standards is aggregate testing carried out to?

Aggregate testing is usually carried out to the BS EN series. The 933 parts cover geometrical properties such as grading and particle shape, the 1097 parts cover mechanical and physical properties including particle density, water absorption and resistance to fragmentation, while the 1367 parts cover soundness and freeze-thaw and the 1744 parts cover chemical properties. Sampling and sample reduction follow BS EN 932.

What does an aggregate supplier need to prove a new source?

A producer proving a source generally needs the full property set the relevant product standard calls up, repeated often enough to show the source is consistent rather than tested once. That usually means grading, shape, fines quality, density and water absorption, plus the durability properties for the end use. The categories a source can declare are then carried through into what customers can specify from it.

What does the grading tell me, and what if the material plots outside the limits?

Grading is the particle size distribution plotted against the envelope in the specification, and it governs how the material compacts, drains and locks together. A curve outside the envelope usually means the stockpile will not behave predictably: too many fines hold water and go soft under plant, too few leave it loose and open. A single failing sample may reflect segregation in the stockpile rather than the source, so where it came from matters.

Why do particle shape and fines matter as well as grading?

Because two materials with the same grading can behave very differently depending on particle shape and on what the fines actually are. Flakiness and shape index identify elongated or flaky particles that fracture under compaction, while the sand equivalent and methylene blue tests separate harmless rock dust from clay that will soften the material once it is wet. Specifications for subbase and concrete aggregate commonly set categories for both.

What are water absorption and particle density used for?

Water absorption measures how much water the aggregate takes into its pores, normally reported over 24 hours, and particle density is the density of the particles themselves. Concrete mix design needs both to get the free water content and batch quantities right, and a high absorption often flags a porous, less durable stone. Both are also used to convert between mass and volume when working out how much material a layer takes.

Which durability test should I ask for: Los Angeles, magnesium sulfate or freeze-thaw?

Ask for whichever your specification names, because they measure different mechanisms. The Los Angeles test measures resistance to fragmentation under mechanical action, magnesium sulfate soundness measures breakdown under repeated salt crystallisation as a proxy for weathering, and freeze-thaw measures loss after freezing cycles. Soundness and freeze-thaw run as cycles over several days, so they take considerably longer than a Los Angeles test and need planning into the programme.

Does crushed concrete or recycled material need any extra testing?

Yes. Alongside the usual physical and durability properties it needs a constituent classification, so the proportions of concrete, masonry, bituminous material, glass and foreign matter can be checked against the limits for the intended use. Recycled material also varies far more from load to load than a quarried source, so specifications normally set a higher testing frequency and a sampling regime to match.

Does a test report let us CE or UKCA mark the material or issue a declaration of performance?

No. Marking and the declaration of performance are the producer's responsibility under the construction products regime, and they rest on a factory production control system assessed by an approved or notified body rather than on individual test results. Test reports support that system and demonstrate a delivered material against a specification, but they do not replace it. CE marking continues to be recognised in Great Britain alongside UKCA marking.

How do we take a sample that actually represents the stockpile?

The sample has to represent the material as a whole, which normally means combining several increments taken from different points rather than one scoop off the face of a stockpile, then reducing it by the BS EN 932 methods. Quantity depends on the tests, since a grading needs far less than a fragmentation or soundness test on a coarse fraction. Tell us the tests and the top size and we will confirm how much to send.

Is aggregate testing covered by your UKAS accreditation?

Hixtra holds UKAS accreditation to ISO/IEC 17025 for the tests listed in its schedule of accreditation, number 8996. Accreditation is specific to the listed methods and scope, rather than to every service. An aggregate suite can contain a dozen separate methods, so send us the list of tests you need and we will confirm the status of each one before anything is booked.

We have a stockpile that needs testing. What do you need from us?

Send the material type and source, the end use or product standard it has to meet, the list of tests or the specification clause, the number of samples and your programme dates. Say whether you need sampling as well as laboratory testing. Cost is driven by the number of tests and samples, sample preparation, any site attendance for sampling and whether the slower durability tests are in the schedule.